I have one, all important question to ask you in response: how many of the assumptions that the designers made about game play does your group follow? The further you stray from that baseline, the less reliable the given metrics become.
Party of 4
Warrior, mage, priest, thief
skulking backstabber thief
tough-as-nails, dumb-as-a-brick warrior
WBL and readily available magic items
The more of these fall through, the less reliable CR, among other things, gets. A skilled GM can compensate for any or even all of these things being different than expected, and I'm not saying you're not skilled enough to do it, but pointing at the book and saying "see, four encounters per day," rings more than a little hollow if that is the only or one of only a few of the other presumptions the game makes you're sticking to.
All that out of the way, heck no. Not past about level 5 or so, anyway.
Up until level 5~7 or so, the dice play a -major- role in -everything- the PCs do. It's part of why I don't like to play or GM for that level range. When the RNG can spike you like a game-winning touchdown ball at pretty much any time, it doesn't matter how competently you play. It's not -hard- it's just random.
After that point, you should have picked up -some- ability to avoid things you can't handle and excell at things you can to the point that the dice aren't everything. You can still get spiked but it's no longer at dangerously high odds and becomes less so with each level.
Mind, that's at bare minimum competence presumed by the designer's guidelines. Top-tier optimizers can get to okay-ish chances at the lowest levels and become... difficult to GM for in later levels, to the point of the game actually breaking down when you hit 9th level spells.
The resource managment portion of the game can throw things off for some players. If you nova the first encounter of the day and still have to go through three more, the last is going to be way tougher than it has to be.
Finally, there's the one simple fact others upthread have pointed out: none of this is prescripted code. You can and should make adjustments until you reach a point that's fun for you and your players. If it's too difficult for your players, soften up unless that would make the game too boring for you. If you're already playing with kid gloves and they're still complaining, try and help them figure out how to perform better. Either way, something's gotta give.